Our brains function through complex and dynamic networks of interconnected neurons. Understanding how this neuronal circuitry is established and regulated is not only the central question of neuron development studies, but also the key to understand the pathogenesis of neurodevelopment disorders. In the aCC motoneuron of Drosophila embryo, our preliminary findings have hinted the connection among the Down syndrome cell adhesion molecule (Dscam1), cytoskeleton activity regulators including Cdc42 effectors, and the positioning and initiating of dendrite growth. Therefore, we hypothesize that Dscam intercellular interaction promotes and positions aCC dendritogenesis through membrane enrichment of Cdc42 effectors. We plan to test this hypothesis using a combination of genetic and super-resolution microscopy methods. Our project consists of three aims: Aim 1 to examine the role of Cdc42 effector membrane accumulation in controlling the position of new dendrites, Aim 2 to elucidate the mechanism for Dscam in aCC to guide the positioning of Cdc42 effectors, and Aim 3 to understand the extracellular cue from partner neurons through Dscam1-Dscam1 interaction. Accomplishing these aims will provide insights into the detailed molecular mechanisms of Dscam function, especially how cell-cell recognition is translated through cytoskeleton dynamics into neuron morphogenesis in CNS, which has been very much under-explored in the central nervous system (CNS).